Fix field type handling in load elimination.

src/hydrogen-load-elimination.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 60 matching lines @@
     switch (instr->opcode()) {
       case HValue::kLoadNamedField: {
         HLoadNamedField* l = HLoadNamedField::cast(instr);
         TRACE((" process L%d field %d (o%d)\n",
                instr->id(),
                FieldOf(l->access()),
                l->object()->ActualValue()->id()));
         HValue* result = load(l);
         if (result != instr &&
             result->type().Equals(instr->type()) &&
-            result->representation().Equals(instr->representation())) {
+            result->representation().Equals(instr->representation()) &&
+            (!result->IsLoadNamedField() ||
+             HLoadNamedField::cast(instr)->map_set()->IsSubset(
+                 HLoadNamedField::cast(result)->map_set()))) {
           // The load can be replaced with a previous load or a value.
           TRACE(("  replace L%d -> v%d\n", instr->id(), result->id()));
           instr->DeleteAndReplaceWith(result);
         }
         break;
       }
       case HValue::kStoreNamedField: {
         HStoreNamedField* s = HStoreNamedField::cast(instr);
         TRACE((" process S%d field %d (o%d) = v%d\n",
                instr->id(),
@@ skipping 436 matching lines @@
   } else {
     // Perform only local analysis.
     for (int i = 0; i < graph()->blocks()->length(); i++) {
       table->Kill();
       engine.AnalyzeOneBlock(graph()->blocks()->at(i), table);
     }
   }
 }
 
 } }  // namespace v8::internal